Acoustic blanket

Payload fairings of launch vehicles are intended to protect payloads, such as satellites to be lifted into orbit, against damage on the launchpad as well as during flight through the atmosphere. Because of their position on the nose of the launch vehicle, payload fairings are generally subjected to strong aerodynamic interactions that generate acoustic energy. Additionally, launch vehicles are subjected to very high noise during lift-off under partial or full thrust. Such intense acoustic loads can damage the payload. If a launch vehicle includes personnel, then consideration must also be given to their protection from these acoustic loads.

The structure of a payload fairing offers some protection against acoustic loads but is generally insufficient so that additional measures are often required. One such measure is to add sound-absorbing materials, such as insulating panels or mats, to the walls of the payload fairing. The design of acoustic protection on payload fairings of launch vehicles, however, needs to consider the high importance of mass and volume, which are critical features for space vehicles. Thus, some measures for protection against acoustic loads may sufficiently block or absorb sound energy, but would be relatively heavy and too large, so that valuable payload accommodation volume and performance would be lost.

Achieving acoustic absorption without increasing the thickness of an absorber and increasing acoustic transmission loss with only an incremental mass increase are both difficult problems, especially in the low frequency range. One way to control low-frequency noise, which generally falls within the frequency range of the above-mentioned acoustic loads, is to use melamine or polyimide foam (or a combination of both) and to increase their thickness in accordance to needed performance. Older launch vehicles used fiberglass. Unfortunately, low frequency acoustic performance of these materials only increases by substantially increasing their thickness (and consequently their mass).

This disclosure describes an acoustic blanket, and methods of its fabrication, to absorb acoustic energy and reduce noise in a launch vehicle. For example, the acoustic blanket may be overlaid on the interior (e.g., inside walls) of a payload fairing of the launch vehicle. Materials and construction of the acoustic blanket allow for a relatively thin and light sound barrier, which are characteristics that are very important for a launch vehicle.

In some embodiments, the acoustic blanket comprises relatively dense vertically-lapped polyester that is overlaid with a lightweight melamine foam. This combination of materials (e.g., a dense material adjacent to a lightweight material) creates an acoustic impedance mismatch between the layers that leads to desired absorption of acoustic energy across a relatively broad range of frequency bands. For a particular example, a dense material having a density of 1.25 pounds per cubic foot (PCF) and a lightweight material having a density of 0.375 PCF may result in a factor of 3.3 impedance mismatch. Noise during the launch of a launch vehicle generally falls within these frequency bands. As explained below, the acoustic blanket has a particular heat seal pattern that allows the acoustic blanket to be relatively soft and flexible, which helps absorb noise. Such flexibility is useful for attaching the acoustic blanket to a curved wall of a fairing or other launch vehicle shapes, for example.

In some embodiments, an acoustic blanket may include a first facing layer that at least partially covers a melamine foam layer, and a polyester layer that at least partially covers the melamine foam layer. In some implementations, the melamine foam may be ultra-light melamine foam and the polyester may be dense vertically-lapped polyester, though claimed subject matter is not limited in this respect. A second facing layer at least partially covers the polyester layer. In other words, a melamine foam layer and a polyester layer are sandwiched between two facing layers, both of which may be Mylar, Kapton, or other similarly thin and flexible material, for example. Air gaps are formed between the polyester layer and the second facing layer and are partitioned from one another by a heat seal pattern between the polyester layer and the second facing layer. The second facing layer may include micro-perforations that allow for movement of air between the air gaps and outside the acoustic blanket.

In some embodiments, a method of fabricating such an acoustic blanket may include bonding the first facing layer to the melamine foam layer so that the first facing layer at least partially covers the melamine foam layer. The polyester layer may then be bonded to the melamine foam layer so that the polyester layer at least partially covers the melamine foam layer. The method also includes placing a second facing layer on the polyester layer so as to at least partially cover the polyester layer, and heat sealing the second facing layer and the polyester layer together in a heat seal pattern. In some implementations, the heat seal pattern forms air gaps between the polyester layer and the second facing layer.

is a cross-section view of a portion of an acoustic blanket, according to some embodiments. Acoustic blanketmay include a first facing layerthat at least partially covers a melamine foam layer, and a polyester layerthat at least partially covers melamine foam layer. As mentioned above, the melamine foam (e.g., layer) may be ultra-light melamine foam and the polyester (e.g., layer) may be dense vertically-lapped polyester, which may provide a number of advantages. For example, the vertically-lapped structure may allow for relatively high flexibility such that the acoustic blanket may bend to conform a curved wall of a fairing, for instance. Additionally, the vertically-lapped structure provides for relatively high acoustic absorption.

A second facing layerat least partially covers polyester layerand these two layers are attached to each other in a heat seal pattern by heat sealing, as described below. First and second facing layerandmay be Mylar, for example. Second facing layerincludes micro-perforations, as illustrated by inset, which is a close-up view of a portion of second facing layerand polyester layer. Illustrated in this close-up view are a heat sealand air gapsbetween polyester layerand second facing layer, and the micro-perforations in the second facing layer. Heat sealis a portion of a heat seal pattern that forms air gapsbetween polyester layerand second facing layer. Air gapsare partitioned from one another by the heat seal pattern, as described below. Micro-perforationsallow for movement of air between air gapsand outside(e.g., exterior to) the acoustic blanket. This heat seal methodology may also be used between the first facing layerand melamine foam.

In some particular implementations, polyester layermay have a density of about 1.25 PCF and a thickness of about 1 inch. Melamine foam (e.g., layer) may have a density of about 0.375 PCF and a thickness in a range of about 3 to 5 inches. The polyester layer (e.g., layer) may be dense vertically-lapped by about a hundred folds per inch, though claimed subject matter is not limited with respect to these example values.

Though not illustrated, in some implementations, facing layersand/ormay wrap around sides of acoustic blanket. These side portions of the facing layers may include micro-perforations, which may be useful for at least partially controlling venting paths of air inside the acoustic blanket. For example, one or both top sheets (e.g., facing layers) of the acoustic blanket may be without perforations while the four sides of the acoustic blanket include perforations. In other implementations, sides of acoustic blanketmay be covered with a Mylar (or similar) tape that adheres to the sides of the polyester and melamine layers. The edges of that Mylar tape may be themselves closed with thinner Mylar tape.

is a top view of a portion of acoustic blanket, illustrating a heat seal patternthat partially bonds second facing layerto polyester layer, according to some embodiments. Heat sealis part of heat seal pattern. As mentioned above, the heat seal pattern forms air gapsbetween second facing layerand polyester layerthat are partitioned by the heat seal pattern. The heat seal process may be a hot-melt process, wherein there may be a heat seal material between the polyester layer and the second facing layer. These two layers do not melt, but instead the seal material between them melts and sticks to both the facing layer and the polyester layer, for example. As mentioned above, a heat seal may also exist between first facing layerand melamine.

In some implementations, the surface area of air gaps(e.g., in a plan view) is substantially greater than the surface area of the heat seal pattern. In other words, and in a particular example, the surface area ratio of air gaps to the heat seal pattern may be greater than about 90% (e.g., an approximate range between 85% and 95%). For a particular example, heat seals (e.g.,) may be about 0.25 inches wide and distances between adjacent heat seals may be about 5 inches. Heat seal patternmay be substantially rectangular or square, comprising vertical pattern portionsand horizontal pattern portions. Such rectangles or squares may be offset from one another in a staggered fashion, as illustrated in, though claimed subject matter is not so limited. Corners of the squares or rectangles may have a rounded corner radius of about 0.25 inches in some implementations.

is a cross-section view of a portionof acoustic blanket, illustrating air gapsand heat seal, which is part of heat seal pattern, according to some embodiments. In a particular implementation, facing layermay be Mylar having a nominal 0.001 inch thickness. There may be tradeoffs between increased strength with protection against tearing and flexibility when selecting a thickness for facing layer.

is a top close-up view of a portionof acoustic blanket, illustrating micro-perforationsin second facing layer, according to some embodiments. For example, micro-perforationsmay have a nominal diameter of about 100 microns and an on-center spacing of about 1.9 mm. Micro-perforationsmay staggered so they are offset by 45 degrees.

In some implementations, second facing layermay comprise a permeable material and need not include micro-perforations. In still other implementations, facing layersandmay not be perforated, as mentioned above. Instead, the sides of acoustic blanketmay be perforated. For example, one or both top sheet (e.g., facing layers) of the acoustic blanket may be without perforations while the four sides of the acoustic blanket include perforations. These latter perforations may have a pattern that is different from the pattern illustrated in. For example, micro-perforations of the sides of the acoustic blanket may be in an orthogonal arrangement of rows and columns (e.g., a rectangular grid pattern) with on-center spacing of about 0.25 inches. The micro-perforations may have a nominal diameter of about 0.043 inches.

is a cross-section view of an acoustic blanketmounted onto a portion of a fairing, according to some embodiments. For example, acoustic blanketmay be the same as or similar to acoustic blanket. As mentioned above, features such as the relatively small heat seal surface area and properties of the individual layers allow the acoustic blanket to be substantially flexible. Such flexibility provides an advantage in that the acoustic blanket may conform to the curvature of a fairing, which may, for example, have a radius of curvature of about three or so meters.

is a flow diagram of a processof fabricating an acoustic blanket, according to some embodiments. For example, the acoustic blanket may be the same as or similar to, described above. Processmay be performed by a fabricator. At, the fabricator may heat seal a first facing layer, such as, and a melamine foam layer, such as, together so that the first facing layer at least partially covers the melamine foam layer. The first facing layer and the melamine foam layer may be bonded together with a heat seal pattern. At, the fabricator may bond a polyester layer, such as, and the melamine foam layer together so that the polyester layer at least partially covers the melamine foam layer. At, the fabricator may place a second facing layer, such as, on the polyester layer so as to at least partially cover the polyester layer. At, the fabricator may heat seal the second facing layer and the polyester layer together in a heat seal pattern (e.g.,) that forms air gaps, such as, between the polyester layer and the second facing layer. In some implementations, there may be a heat seal pattern on both sides of the acoustic blanket. For example, the heat seal pattern between the first facing layer and the melamine foam layer may be the same as or similar to the heat seal pattern between the second facing layer and the polyester layer. Such heat sealing on both sides of the acoustic blanket (e.g., both the back and the front facing layers are attached to their underlying blanket layers with a heat sealing pattern) may help contribute to the overall flexibility of the blanket.

is a graphof acoustic transmission loss through a traditional acoustic barrier and an acoustic blanket, as described herein, as a function of frequency, according to some embodiments. Graphwas generated from experimental data acquired for a four inch thick sample of traditional melamine foam, represented by plot, and a four inch thick sample of an acoustic blanket similar to or the same as, represented by plot. As illustrated in graph, the acoustic blanket outperforms the traditional melamine by having a substantially higher transmission loss between 100 Hz and 4000 Hz.

is a graphof the acoustic absorption coefficient of a traditional acoustic barrier and an acoustic blanket, as described herein, as a function of frequency, according to some embodiments. Graphwas generated from experimental data acquired for a four inch thick sample of traditional melamine foam, represented by plot, and a four inch thick sample of an acoustic blanket similar to or the same as, represented by plot. As illustrated in graph, the acoustic blanket outperforms the traditional melamine by having a substantially higher acoustic absorption coefficient from below 100 Hz to past 10,000 Hz.

The foregoing description, for purposes of explanation, used specific nomenclature to provide a thorough understanding of the disclosure. However, it will be apparent to one skilled in the art that the specific details are not required in order to practice the systems and methods described herein. The foregoing descriptions of specific embodiments or examples are presented by way of examples for purposes of illustration and description. They are not intended to be exhaustive of or to limit this disclosure to the precise forms described. Many modifications and variations are possible in view of the above teachings. The embodiments or examples are shown and described in order to best explain the principles of this disclosure and practical applications, to thereby enable others skilled in the art to best utilize this disclosure and various embodiments or examples with various modifications as are suited to the particular use contemplated. It is intended that the scope of this disclosure be defined by the following claims and their equivalents.